Device semaphore granted and waited

The “Device Semaphore Granted” and “Device Semaphore Waited” categories report the number of times that a request for a device semaphore was granted immediately and the number of times the semaphore was busy and the task had to wait for the semaphore to be released. The “% of total” column is the percentage of times the device the semaphore was granted (or the task had to wait) as a percentage of the total number of device semaphores requested. This data is meaningful for SMP environments only.

When Adaptive Server needs to perform a disk I/O, it gives the task the semaphore for that device in order to acquire a block I/O structure. On SMP systems, multiple engines can try to post I/Os to the same device simultaneously. This creates contention for that semaphore, especially if there are hot devices or if the data is not well distributed across devices.

A large percentage of I/O requests that waited could indicate a semaphore contention issue. One solution might be to redistribute the data on the physical devices.